Mechanism and application of critical micelle concentration (CMC) detection using multimode optical fiber

A new detection method of critical micelle concentration (CMC) using a multimode optical fiber is proposed for an industrial application. A part of the cladding of the fiber is removed as a sensing region. Each sensing region of 13 cm long on a silica core of 1.0 mmφ diameter and plastic core of 1.5 mm is immersed into a surfactant solution. The CMC result is presented corresponding to the particular concentration at which outputs from the optical fiber abruptly increase. It is also found that for using small diameter of 0.2 mmφ silica core and 0.5 mmφ plastic core and 1-cm-long sensing region has almost the same sensitivity as a 13-cm-long sensing region of the preceding large core, which suggests that the thinner the core, the higher the sensitivity. With increasing surfactant concentration below the CMC, the refractive index is almost constant and the optical output has no change, but the outputs abruptly increase near the CMC although the refractive index of the solution constant. The CMC detection using an optical fiber is based on the principle of adsorption effect. The data can be sent to a remote process controller through this fiber line in a real time.